1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing equipment and, more particularly, to a container cart for use in a cleanroom environment.
2. Prior Art
In the manufacture of VLSI and ULSI semiconductor integrated circuit devices, it is essential that the cleanroom environment in which these devices are fabricated be kept as clean as possible. This is especially important in the instance where these semiconductor "chips" have device or interconnecting line dimensions of less than one micron. Since these submicron dimensioned devices are fabricated in a cleanroom environment on the order of Class 1 or better, it is imperative that any contamination causing activity be either removed or isolated from the immediate processing area. A cleanroom is rated Class 1 if it contains no more than one 0.5 micron or larger particle per one cubic foot of space.
One technique being employed in today's "cleanrooms" is to physically isolate the maintenance operation from the chip fabrication operation. In order to achieve this, today's cleanrooms incorporate maintenance corridors which are physically separated from the portion of the cleanroom where the chip fabrication occurs. The various chip processing equipment is then positioned so that the front of the equipment, which is utilized for chip manufacturing, faces the fabrication environment, while the back of the equipment resides in or faces the maintenance corridor. When this particular equipment requires servicing, maintenance personnel will access and service the equipment from the maintenance corridor so that any contaminants introduced or dislodged by this servicing activity will be retained in the maintenance corridor and will not be introduced into the chip manufacturing side of the cleanroom.
However, although this is a sound technique for reducing the possibility of contaminating the cleanroom environment, there are instances when this approach is not workable. In some instances, a particular servicing task for the equipment requires entry to or within the chip fabrication environment. For example, when the front panel of the equipment needs to be removed for service access or, when the equipment resides completely within the fabrication environment, maintenance activities will be forced to coexist with chip fabrication.
In other instances, either preventative or corrective maintenance will require certain assemblies of a particular piece of equipment to be dismantled. The equipment being dismantled, can potentially introduce contaminants into the cleanroom. For example, in a particular piece of equipment used to deposit tungsten onto a semiconductor wafer, the wafer is subjected to very high temperatures in the range of 400.degree.-490.degree. C. The tungsten tends to deposit on the tooling and the chamber of the reactor. After prolonged use, this deposited tungsten residue needs to be removed from the reactor components. Because the equipment itself cannot be removed from the cleanroom environment without causing a major disruption of the fab operation, maintenance personnel typically dismantle the reactor components in the cleanroom in order to service the system. However, the reactor must necessarily be cooled down before maintenance personnel can physically dismantle the reactor assembly. One unfortunate result of permitting the equipment to be cooled to room temperature prior to performing the maintenance is that the residual tungsten deposited within the chamber tends to flake off. This results in the introduction of significant quantities of tungsten contaminants into the cleanroom environment.
Additionally, further contaminants are introduced into the cleanroom environment from the actions of the maintenance personnel in servicing the equipment. For example, tools and equipment which are typically stored outside of the cleanroom must necessarily be brought into the cleanroom, for not only the removal and repair of the assembly, but for required diagnostic functions after the assembly has been cleaned and replaced back in the equipment.
Thus, it is necessary that in such instances where the maintenance activity must occur in the cleanroom, additional care must be exercised to reduce or prevent contamination from occurring as a result of such activity. It is preferable to remove any portion of such activity from the cleanroom, if possible, in order to reduce the risk of cleanroom contamination. The present invention provides for an apparatus for permitting the bulk of the maintenance activity to be performed outside of the fabrication and/or the maintenance portion of the cleanroom.